Dynamic multiplier



, 30, 1934- J. H.- HAMMOND, JR 1,979,037

DYNAMIC MULTIPLIER Original Filed May 5, 1930 O'lill FIG. I.

A TTORNE Y.

Patented Oct. 30, 1934 UNITED STATES PATENT OFFICE DYNAIHIC MULTIPLIER Application May 3, 1930, Serial No. 449,505 Renewed March 2, 1933 26 Claims. (Cl. 179-1001) This invention relates to an improved system for controlling the amplification factor or gain ratio of an amplifier in accordance with the strength and rate of change of the applied energy.

The invention relates particularly to a system of amplification which will accentuate any sudden change of energy and which will also respond to gradual increases or decreases of the average energy level, thus increasing the energy range so as to produce greater energy variations.

The invention provides a system for increasing the-energy range of an amplifying system which is controlled by the average values of input energy over different intervals of time. The intervals of time may be of sub-audible frequency corresponding to the duration of syllables or sudden percussions or they may be of longer duration so as to give the-average value during the speaking of several words or the playing of several measures.

This is accomplished in accordance with the present invention by the use of an amplifying system which is controlled by two circuits one of which responds to a. rapid rate of energy change an? the other to a prolonged rate of energy change.

The present invention provides for controlling the operating characteristics of a space discharge amplifier in accordance with the strength of the applied signal, so that the amplifying efficiency of this device is greater for strong signals than for weak signals. The efliciency is controlled by the volume of input energy which is applied to two or more control circuits operating at different sub-audible frequencies. These circuits control the impedance of the space discharge amplifier so that the impedance is reduced'for a strong signal whereby a greater amplification efficiency is obtained by strong signals than by weak ones.

This system is particularly adapted for use in connection with the energy received from a phonograph pick-up or a photographic sound record.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which Fig. 1 illustrates diagrammatically one type of circuit for carrying out the present invention;

Fig. 2 is a schematic diagram of a modified form of the invention; and

Fig. 3 shows two curves which illustrate the gain ratio of an amplifier constructed in accordance with the pres nt invention.

Like reference characters denote like parts in the several figures of the drawing.

In the following description and in the claims parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring more particularly to the drawing, Fig. 1 shows an amplifying system which receives its energy from a phonograph pick-up 10, or a photoelectric cell 11. This cell receives light from a lamp 12, which is energized from a source of power 13. The light from this lamp is focused by a lens 14, through an aperture 15, in an aperture plate 16, upon the sound record of a moving film 17. The light which passes through this film then impinges upon the photoelectric cell 11. This cell is connected through a transformer 18 to two contacts 21, of a double pole, double throw switch 22, the other contacts 23 of which are connected to the phonograph pick-up 10.

The blades of the switch 22 are connected to the primary of a transformer 24, the secondary of which is connected in the input circuit of a space discharge means 25, the output circuit of which is connected to the primary of a transformer 26. Across this primary is a resistance 2'7, for the purpose of keeping the input impedance of the transformer practically constant and independent of the impedance change between the plate and filament of the device 25. The secondary of the transformer 26 is connected to the input circuit of a pushpull amplifier 28, the output circuit of? which is connected to the primary of a transformer 31. The secondary of this transformer is connected to the moving coil of a loud speaker'32, the field 33 of which is energized from a power source 34.

Across the secondary of the transformer 24 is connected the input circuit of a space discharge device 35. The output circuit of this device is connected to the primary of two transformers 35 and 37. The secondaries of these transformers are connected through tap switches 38 and 39 and through rectifiers 41 and 42 to the grid return lead of the space discharge device 25. In

full line curve 51 in Fig. 3.

this lead and across the rectifiers 41 and 42 in series with secondaries of transformers 36 and 3'7 are resistances 43 and 44 which are shunted by condensers 45 and 46 respectively.

The resistance 43 is of very high order; for example, of 500,000 ohms and the capacity 45 is comparatively large; for example, 4 microfarads. The resistance 44 is relatively lower; for example, 50,000 ohms and the capacity 46 is relatively smaller; for example, 6 microfarad.

A blocking condenser 47 is in the grid lead of the space discharge device 35 and a high valued coupling resistance 48 is connected between the grid and filament of this device. The grid return lead of amplifier 25 is connected to a potentiometer 49. The various space discharge devices have associated therewith sources of filament current, space current, and grid potential which are connected in a manner well-known in the art.

In the operation of the form of the invention shown in Fig. 1, the switch 22 is thrown up if the photographic sound record is used, and is thrown down if the phonograph is to be operated. In either case the energy received passes through the primary of the transformer 24 from the secondary of which the energy passes to the space discharge amplifier 25, thereby causing this to function in a well-known mannerso as to produce corresponding fluctuations of current in the output circuit of this device. At the same time some of the energy from the secondary of .the transformer 24 is passed to the space discharge device 35 where it is amplified and passed through the primaries of the transformers 36 and 37. The current from the secondaries of these transformers is rectified by means of rectifiers 41 and 42 which causes current to flow in the direction of the arrows through the resistances 43 and 44.

As the capacity 45 is large it takes a considerable length of time for thesecondensers to be charged, and as the resistance 43 is large it takes a correspondingly long time for these condensers to be discharged. This causes a gradual decrease in the negative potential on the grid of the space discharge device 25, and a gradual decrease of the impedance of this device which in a well-known manner will increase the plate current, thus increasing the energy fed to the primary of the transformer 26. This, however, would be of gradual increase and decrease as shown by the In this way any energy change extending over a comparatively long period of time, such for example, as the speaking of several words or the playing of several measures, will produce an amplification ratio or gain ratio in the space discharge device 25 in accordance with the average energy level during this period.

The current from the secondary of the transformer 37 will be rectEfied by the rectifier 42 causing the condenser 46 to be charged. This condenser, however, being of smaller capacity than condenser 45 will be charged comparatively rapidly and as the resistance 44 is smaller than resistance 43, it will be discharged at a rapid rate. In this way any rapid fluctuations of received energy will cause rapid changes of potential to be applied to the grid of the space discharge device 25, thus causing a rapid change of amplification in this device, such for example, as *ithat shown by the dotted lines 52 of Fig. 3.

The operating characteristics of the space dis: charge amplifier are such that its amplifying efficiency is greater for strong signals than for weak signals. In this way a greater range variation of current is produced thanthat originally present in that of the received energy.

It may be found desirable to control the rela-' tive amplification of the tone current in accordance with rapid fluctuations of energy with respect to the amplification for gradual energy fluctuations. This may 'readily be accomplished by proper manipulation of the switches 38 and 39 so as to vary the relative amount of energy taken from the secondaries of the transformers 36 and 37 respectively. This will produce different potential variations across the resistances 43 and 44 which in turn will produce different amplification control for the rapid and slow fluctuations.

In this way it is seen that this device responds to both a rapid variation of received energy, thus producing a rapid response in the loud speaker device 32, and also to a more gradual variation of received energy thus raising or lowering the.

average volume produced'by this device.

in Fig. 2 the secondary of the transformer 24 is connected inthe input circuit of the space d'scharge means 25, the output circuit of which is connected in this instance to the primary of a transformer 55, across which is a resistance 56. The secondary of the transformer 55 is connected in the input circuit of a space discharge device 57, the output circuit of which is connected to the primary of the transformer 26, across which is a resistance 27.

Across the secondary of the transformer 24 is connected the input circuit of the space discharge device 35. The output circuit of this device is connected to the primary of the transformer 36. The secondary of this transformer is connected through the rectifier 41 to the input filament lead of the space discharge device 25. In this lead and across the rectifier 41 in series with the secondary of transformer 45 is the comparatively high resistance 43 which is shunted by the large condensers 45. A blocking condenser 47 is in the grid lead of the space discharge device 35 and a high resistance 48 is connected between the grid and filament of this tube. The input filament lead of amplifier 25 is connected to a potentiometer 49.

Across the secondary of the transformer 55 is connected the input circuit of a space discharge device 61. The output circuit of this device is connected to the primary of the transformer 37. The secondary of this transformer is connected through the rectifier 42 to the input filament lead of the space discharge device 57. In this lead and across the rectifier 42 in series with secondary of transformer 3'7 is the comparatively low resistance 44 which is shunted by the small condenser 46. A blocking condenser 62 is in the grid lead of the space discharge device 61 and a high resistance 63 is connected between the grid and filament of this tube. The input filament lead of amplifier 5'7 is connected to a potentiometer 64.

The various space discharge devices have associated therewith sources of filament current, space current and grid potential which are connected in a manner well-known in the art.

In the operation of the form of the invention shown in Fig. 2 the energy received by the transformer 24 passes to the space discharge amplifier 25. At the same time some of the energy from the secondary of the transformer 24 is passed to the space discharge device 35, where it is amplified and passed through the primary of the transformer 36. The current from the secondary of this transformer is rectified by means of the rectifier 41 which causes current to flow in the direc- -5 tion of the arrow through the resistance 43.

As the capacity 45 is large it takes a considerable length of time for these condensers to be charged, and as the resistance 43 is large it takes a correspondingly longtime for these condensers to be discharged. This causes a gradual building up of positive potential on the grid of the space discharge device 25, and a gradual decrease of the impedance of this device which in a wellknown manner will increase the plate current, thus increasing the energy fed to the primary of the transformer 55. This, however, would be of gradual increase and decrease as shown by the full line curve 51 in Fig. 3.

In this way any energy change extending over a comparatively long period oftime, such for example, as the speaking of several words or the playing of several measures, will produce an amplification ratio in the space discharge device 25 in accordance with the average energy level during this period.

Energy from the secondary of the transformer 55 passes to the space discharge amplifier 57..

At the same time some of the energy from the secondary of the transformer 55 is passed to the space discharge device 61 where it is amplified and passed through the primary of the transformer 37. Th current from the secondary of this transformer is rectified'by means of the rectifier 42 which causes current to flow in the direction of the arrow through the resistance 44.

As the condenser 46 is smaller than the condenser 45 it will be charged comparatively rapidly and as the resistance 44 is smaller than the resistance 43 it will be discharged at a more rapid rate. In this way any rapid fluctuations of received energy will cause rapid changes of positive potential to be applied to the grid of the space discharge device 57, thus causing a rapid change of amplification in this device; such for example, as that shown by the dotted line 52 of Fig. 3.

In this way energy which extended over a comparatively short period of time; such for example, as the duration of syllables or sudden percussions will produce an amplification ratio in the space discharge device 57 in accordance with these rapid fluctuations.

The system shown in Fig. 2 produces the same results as that shown in Fig. 1 except that the amplifying control systems, are in ,cascade instead of being in parallel as shown "in Fig. 1.

It will be noted that in the above described system the amplifier is so operated that the amplification factor or gain ratio is controlled by,

the average value of the input signal over a plurality of predetermined time intervals. This permits the amplifier to be controlled in accordance with rapid changes in volume, such as syllables or single notes,'or in accordance with sustained changes in volume which may occur over a plurality of words or through several'measures. The relative efiect of the various time intervals may be varied to cause the reproduced sound to retain its original quality and dynamics. The invention accordingly provides for expanding the volume range or multiplying the dynamics of the signal being amplified so that it is caused to approximate its original form.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a phonographic system, the method of operating a space discharge amplifier for the amplification of audiofrequency signals which comprises simultaneously varying the gain ratio of said amplifier in accordance with the average value of the input signal taken over a plurality of different predetermined time intervals.

2. In a phonographic system, the method of operating an amplifier for amplifying audioirequency signals which comprises simultaneously varying the gain ratio of said amplifier at a plurality of different sub-audiofrequencies in accordance with the changes in average volume of the input signal at said frequencies.

3. In a phonographic system, the method of operating an amplifier for the amplification of audiofrequency signals which comprises simultaneously varying the gain ratio of said amplifier directly as the average volume of the signal at a plurality of different sub-audiofrequencies whereby the volume range of the signal is expanded in the output of said amplifier.

4. In a phonographic system, the method of operating an amplifier for the amplification of audiofrequency signals which comprises simultaneously controlling the amplification characteristics of said amplifier in accordance with rapid changes of signal volume and in accordance with the average signal volume over a substantial interval of time.

5. In a phonographic system, the method of operating an amplifier for the amplification of audiofrequency signals which comprises varying the amplification characteristics of said amplifier in accordance with rapid changes in signal volume whereby the volume range of the output of said amplifier is expanded, and simultaneously controlling the amplification characteristics of the amplifier in accordance with the average ,signal value over a selected period of time whereby a sustained increase in volume increases the gain ratio of said amplifier.

6. A phonographic system comprising an amplifier having variable amplification characteristics, a means for impressing an audiofrequency signal on said amplifier, and means for simultaneously controlling the amplification characteristics thereof in accordance with the rapid changes in volume of said signal and with the average volume of said signal over a predetermined period of time whereby the volume range in the output of said amplifier is expanded.

7. A phonographic system comprising a space discharge amplifier having a control element and means for simultaneously varying the biasing potential of said control element directly as the average value of the input signal over a plurality of different time intervals.

8. A phonographic system comprising a space discharge amplifier having a control element, a plurality of resistances connected in series with said element, and means for passing a current through said resistances proportional to the average value of the input signal taken simultaneously over difierent time intervals whereby the potential of the control element is varied and the gain ratio of said device is so controlled as to expand the volume range of the amplified signal.

9. A phonographic system comprising a space discharge amplifier having a control element, a

plurality of resistances connected in a series in the circuit of said control element, capacities connected in parallel with said resistances, and means for impressing upon each of said resistances a potential which is proportional to the volume of the impressed signal, said condensers and resistances being of such values that the current passing through one of said resistances varies in accordance with rapid fluctuations in signal volume, and the current in the other of said resistances varies in accordance with sustained fluctuations in signal volume, the potential drop in said resistances being in such direction that the amplification factor of said amplifier varies directly as the volume of the input signal.

10. A phonographic system comprising a space discharge amplifier having a control element, means for simultaneously varying the biasing potential of said control element directly as the average change in input signal at a plurality of different sub-audiofrequencies.

11. A phonographic system comprising a variable impedance amplifier and means for simultaneouslyvarying the impedance thereof at a plurality of different sub-audiofrequencies by an amount proportional to the average value of the input signal and means for. preventing the changes in impedance 0! said amplifiers from affecting the transmission characteristics of the subsequent apparatus.

12. A phonographic system comprising a space discharge amplifier having a control element, a

, plurality of resistances connected in a series in the circuit of said control element, capacities connected in parallel with said resistances, a rectifier associated with each of said resistances and means for impressing on each rectifier a potential which is proportional to the volume of the impressed signal, said condensers and resistances being of such values that the current passing through one of said resistances varies in accordance with rapid fluctuations in signal volume and the current in the other of said resistances varies in accordance with sustained fluctuations in signal volume, the potential drop in said resistances being in such direction that the amplification factor of said amplifier varies directly as the volume of the input signal.

18. A phonographic system comprising an amplifier having variable amplification characteristics, a means for impressing an audiofrequency signal on said amplifier, means for simultaneously controlling the amplification characteristics thereof in accordance with the rapid changes in volume of said signal and with the average volume of said signal over a predetermined period of time so that the volume range in the output of said amplifier is expanded, and means for controlling the relative effectof said control means.

14. A phonographic system comprising a plurality of stages of amplification connected in cascade, a control circuit associated with each of said stages and. operated in accordance with the strength of the input signal to the respective stages, said control circuit operating to automatically vary the gain ratio of the associated stage in accordance with the strength of the input signal so that the volume range or the signal in the output circuit of each stage is expanded, the control circuits of the various stages operating simultaneously in accordance with the average value of the impressed signal over different predetermined periods of time.

15. A phonographic system comprising a plurality of space discharge amplifiers connected in cascade, each having a resistance in the circuit of the control element thereof, a control circuit operated in accordance with theinput signal for each of said stages and adapted to pass current through said resistances in a direction such that the potential drop opposes the normal biasing po tential of the respective devices and means associated with said resistances whereby the currents in said resistances vary in accordance with the average value of the signal in the respective input circuits over predetermined time intervals.

16. In a phonographic system, the method of transmitting audiofrequency energy which comprises modifying the dynamics of the audiofrequency energy simultaneously according to a plurality of difierent functions of the input energy.

17. In a phonographic system, the method of transmitting audiofrequency energy which comprises changing the volume ratio of the audiofrequency energy according'to the average value of the audiofrequency energy taken over a comparatively short time interval and simultaneously therewith, also according to the average value of the audiofrequency energy taken over a longer to control said dynamic modifier by-the energy from said reservoirs, and a translating device fed by said dynamic modifier.

19. In a phonographic system, a thermionic dynamic amplifier, a sound record, a pick-up device ior said record feeding said dynamic amplifier, a telephone receiver fed by said dynamic amplifier, a control net-work of timing capacitances and leakage resistances having a plurality of different time constants receiving energy from said pick-up device, and means to control the gain ratio of said dynamic amplifier by said control net-work.

20. In a phonographic system, a thermionic dynamic amplifier, a sound record, a pick-up device for said record feeding said dynamic amplifier, a telephone receiver fed by said dynamic amplifier, a plurality of timing circuits made up of capacitances and leakage resistances having a plurality of difierent time constants receiving energy from said pick-up device, and means to control the gain ratio of said dynamic amplifier by said timing circuits.

21. In a phonographic system,asource of audiofrequency energy, a dynamic modifier fed by said source to change to volume ratio of said audiofrequency energy, a control path receiving some of the energy from said source having a plurality of energy reservoirs for storing up energy averaged over a plurality of different time intervals, means to control said dynamic modifier by the energy from said reservoirs, means'for adjusting the relative amounts of energy impressed on said modifier from said reservoirs, and a translating device fed by said dynamic modifier.

22. In a phonographic system, asource of audiofrequency energy, a dynamic amplifier fed by said source, a loud speaker fed by said amplifier, a control circuit receiving some of the energy from said source and having rectifying devices, a plu-- rality of timing circuits comprising capacitances and resistances having difi'erent time constants fed by said rectifying devices, and means to adjust the relative amounts of energy fed by said capacitances to control the gain ratio or said dynamic amplifier.

23. In a sound record system, the method of translating audiofrequency energy which comprises amplifying said energy and varying the amplification thereof according to a plurality of functions of the input energy.

24. In a sound record system, the method of translating audiofrequency energy which comprises picking up said energy, amplifying it, varying the amplification thereof according to a first function of the input energy, simultaneously varying the amplification thereof according to a second function of the input energy and applying the amplified energy to a translating device.

25. In a sound record system, the method or translating audiofrequency energy which comprises picking up said energy. amplifying it, varying the amplification thereof according to relatively slow changes in the intensity of the input energy, simultaneously varying the amplification thereof according to relatively rapid changes in the intensity of the input energy and applying the amplified energy to a translating device.

26. In a sound record system, a first translating device, an amplifier and a second translating device fed by said amplifier, said amplifier being controlled simultaneously by the audiofrequency energy from said first translating device according to its instantaneous value, its value averaged over a short period of time and its value averaged over a longer period of time.

JOHN HAYS HAMMOND, JR. 

